A study in mice suggests that antiobiotics could harm children's gut bacteria
leaving them prone to obesity and diabetes

Giving children common antibiotics may cause obesity by altering bacteria in their gut, according to new research.

A study mimicking use of the drugs in babies found mouse pups put on weight and developed bigger bones.

The make up of trillions of bugs in their intestinal tract, known as the microbiome and vital for a healthy immune system, also altered.

The findings published in Nature Communications follows an analysis last year of more than 64,500 youngsters that found those receiving antibiotics at least four times before the age of two were more likely to be obese by the time they were five.

The researchers administered three short courses of two of the most common antibiotics prescribed to children, including amoxicillin, to the mice - the same therapeutic dose the average human receives in the first two years of life.

Professor Martin Blaser, of New York University, said although the study was limited to mice, the results agree with many others pointing toward significant effects on children over exposed to antibiotics.

He noted the cumulative data could help shape guidelines governing the duration and type of paediatric prescriptions.

Prof Blaser said: "We have been using antibiotics as if there was no biological cost."

The average child in the UK has taken ten courses of the drugs by the age of 16.

The study supports previous research by Prof Blaser's group suggesting antibiotic exposure during a critical window of early development disrupts the bacterial landscape of the gut and permanently reprogrammes the body's metabolism, setting up a predisposition for obesity.

It found short, high doses of tylosin, which is not prescribed to children but represents another common class called the macrolides which are, had the most pronounced and long lasting effect on weight gain.

Meanwhile amoxicillin, which is popular among doctors because it acts against a broad range of bacteria that cause disease, had the biggest effect on bone growth, a prerequisite for increased height.

Extensive analysis of the lab animals' found both antibiotics also disrupted the gut microbiome.

Prof Blaser said: "They changed the ecology of the microbiome in terms of the richness of the organisms, the diversity, and also what we call the community structure, or the nature of its composition."

The drugs altered not only the bacterial species, but also the relative numbers of microbial genes linked to specific metabolic functions.

Tylosin had a much bigger impact on the maturity of the gut bugs than amoxicillin.

Dr Laura Cox said: "We also see the effect is cumulative.

"So the number of courses of antibiotics matters. We get a little interruption of the maturation process after the second course of antibiotics, and then we have even more interruption after three courses."

The accumulating evidence, they stress, highlights the need for better awareness of the potential downsides of antibiotic overuse.

It is believed antibiotics may kill some bacteria found in the stomach.

Previous research has shown good bacteria in the gut can stop hunger pangs, preventing overeating. Another theory is the drugs change which foods taste good, or stop children being active due to side effects.

Before the age of two children get more fevers and similar illnesses, and it is the most common age for ear infections, which are normally treated with antibiotics.